Migration to Scala 3

[WojciechMazur]

This PR contains a mostly complete migration from Scala 2.13 to Scala 3 (3.2.1 current latest)
General status:

• All projects main/test sources compile with Scala 3
• There are 3 failing test suites - I'm not sure if those are semantic changes in the produced code or problems with the local environment:
  • com.normation.rudder.rest.TestRestFromFileDef
  • com.normation.rudder.services.policies.write.WriteSystemTechniquesTest
  • com.normation.rudder.services.policies.write.WriteSystemTechniques500Test

During the migration we've spotted some bugs in compiler. Most of them were mitigated to allow for compilation. Bug fixes for them would probably be shipped in either 3.2.2 or 3.3:

• Overloaded method taking value class leads to unexpected typer error scala/scala3#16467
• Compiler crash when trying to use object with self reference in multi stage compilation scala/scala3#16437
• Regression in parsing XML syntax scala/scala3#16458
• Cannot use Scala 2.13 traits defining private case class  scala/scala3#16443

The most notable changes:

• fastparse is not yet published for Scala 3. It is using macros to implement parsers to all definitions of parsers were move to temporal utils-parser and rudder-parsers submodules. AFAIK most on the work in terms of fastparse for Scala3 is mostly done (Scala 3 support com-lihaoyi/fastparse#262), so probably we should await a new release of it soon. At that point temporal modules can be removed
• sealerate library is Scala2 only - it's usages were replaced with redefinition of sealed traits with enums. This change can be potentially replaced with manual enumeration of possible cases or using a macro/typeclass derivation.
• There seemed to be problems with specs2 - AFAIK Specs 4.x are having some problems with Scala 3 due to the changes in implicits resolution and syntax changes. I would recommend migration to Specs2 5.x whenever possible - it is only published for Scala 3
• Chimney is not yet published for Scala 3. As a replacement Ducktape was used.
• silencer plugin is not published for Scala 3. Since Scala 2.13 it can be safely removed with scala.annotation.nowarn All usages of nowarn were replaced with this annotation, however probably most of its usages can probably be removed
• Due to the Dotty issue #16443 usages of Serialization for NoTypeHints were replaced with DefaultFormater it should have the same semantics.
• Over 500 usages of final modifier used on objects were removed. All objects are by definition final. Each final object was generating a warning and though made compilation logs unreadable. This change can be safely cherry picked to Scala 2.13 build
• Most of the safe warnings were resolves: these were typically missing parentheses for the typed parameters of lambdas.
• There is still quite large number of high priority warnings - especially in area of NonLocalReturns and usages of scala.reflect.Manifest. These issues should be resolved in the future as they might impact performance.

Becouse of the large amount of changes I recommend reviewing changes based on the commits and not total amount of changes. It would be easier that way. I've tried to group most of the closely related changes together.

[fanf]

Backported scala 2 source compatible changes in #4789

[etorreborre]

I would recommend migration to Specs2 5.x whenever possible - it is only published for Scala 3

@WojciechMazur @fanf is this something I can help with? I tried to checkout this branch and make it compile, I had several compilation errors like

No given instance of type zio.Trace was found for parameter trace

(while running webapp/sources/ldap-inventory> mvn test for example). Is that something that is supposed to work on that branch and I have something wrong in my environment or commands?

[fanf]

Closing this draft, this is handled elsewhere (in several elsewhere). Thanks again for the help, without it, we would have been able to bootstrap that.

[fanf]

oh wow @etorreborre - sorry, I totally missed your almost-one-year old comment. I think it's OK, but @mbaechler might ask you questions at some points if he discovers problems.

[etorreborre]

@fanf no worries. @mbaechler don't hesitate to come back to me.